Most cases of hepatitis arising from blood transfusion are viral-inducted, and distinguishable from other forms of virally-associated liver diseases caused by known hepatitis viruses such as hepatitis A virus (HAV) and hepatitis B virus (HBV). The etiological agent(s) of said Non-A, Non-B hepatitis (NANBH) has long been sought by many research groups and is presently believed to be the hepatitis C virus (HCV). Post-transfusion hepatitis (PTH) occurs in approximately 10% of transfusion patients, and NANBH accounts for up to 90% of these cases. The major problem in this disease is the frequent progression to chronic liver damage (25-55%). Therefore, the demand for sensitive, specific methods for detecting HCV in contaminated blood or blood products is significant.
The hepatitis C virus (HCV) was first identified by molecular cloning and characterization of its RNA genome by Choo, et al. (Science 244: 359-362, 1989). A specific assay using the HCV antigen, designated C100-3, was synthesized using recombinant DNA methods in yeast and detects the antibody of HCV (Science 244: 362-364). A detailed description regarding the genome of HCV, the cDNA sequences derived therefrom, and polypeptides derived from the HCV genome or HCV cDNA as well as methodologies relating to such subject matter, was given in EP 0 318 216 A1 in the name of Chiron Corporation. In particular, the European patent provides a synthesized polypeptide, C100-3, containing 363 viral amino acids which can be used for the detection of HCV antibodies. Now, kits for detecting HCV antibodies on the basis of C100-3 have been commercialized by Abbott Laboratories.
As suggested in the above European patent, HCV may be a flavivirus or flavi-like virus. Generally, with respect to morphology, a flavivirus contains a central nucleocapsid surrounded by a lipid bilayer. It is believed that hepatitis C virus protein is composed of structural proteins including a nucleocapsid (core) protein (C), two glycosylated envelope proteins (E1, E2) and nonstructural proteins (NS1-5). However, the corresponding virus has not yet been isolated nor characterized. It is only confirmed that said C100-3 disclosed by Choo et al. is a protein encoded by part of the nonstructural regions 3-4 of the HCV genome.
Besides, an enzyme-linked immunosorbent assay (ELISA) has also been developed for serological diagnosis of hepatitis C virus (HCV) infection, by using the HCV core protein (p22) synthesized by a recombinant baculovirus by Chiba, et al. (Proc. Natl. Acad. Sci. USA 88:4641-4645, 1991). It was found that C100-3 antibody was not detected in all post-transfusion NANBH cases, probably because of the delayed response to C100-3 antigen. Such delayed response was considered to be due to the fact that the C100-3 is an HCV nonstructural protein. However, Chiba, et al. used an unglycosylated 22-kDa nucleocapsid (core) protein, and established an antibody detection system to develop a specific sensitive method for diagnosing HCV infection.
The invention discloses a DNA molecule coding for an HCV core antigen protein and provides an alternative HCV antibody assay.